The present invention relates generally to recovery of hydrocarbon gas and liquids from a sub-sea wellbore, and, more particularly, the invention relates to technology for separation of contaminants from hydrocarbon gases and liquids utilizing a sub-sea membrane separation system with temperature control.
Hydrocarbon gases and liquids are recovered from underground wellbores by drilling a wellbore into a hydrocarbon gas or liquid formation and withdrawing the materials under reservoir pressure or by artificial lifting. The fluids withdrawn from the reservoir consist of a combination of hydrocarbon liquids and gases, water, sediments, and other contaminants. The water fraction is commonly referred to as produced water. This fraction, although small at the early stages of oil extraction from most fields, grows over the years and could constitute the majority (up to about 90%) of the fluid that is withdrawn from the reservoir.
The current recovery technology involves removing the hydrocarbon and any contaminants including water and sediments which are present from the wellbore, and separating the contaminants from the hydrocarbon above ground or on the ocean surface. This method of separation is costly. Disposal of the removed contaminants may also present environmental problems. The contaminants which may be produced include carbon dioxide, nitrogen, water vapor, hydrogen sulfide, helium, other trace gases, water, water soluble organics, normally occurring radioactive material and others.
Membrane technologies have been developed which separate materials by allowing the selective passage of specific materials through the membrane. One example of a membrane separation system for separating oil and water downhole is described in Price, U.S. Pat. No. 4,296,810. It is desirable to place these membrane materials downhole or on the sea floor to remove the contaminants at the sea floor level and avoid the cost-intensive process of lifting, separating, and disposing of the contaminants. However, the location of these membrane materials downhole or on the sea floor results in a number of potential difficulties including exposure of the membranes to high temperatures and harsh conditions, which are not suitable for many membrane materials.
A membrane""s permeability and selectivity for hydrocarbon gases and liquids are material properties of the membrane itself, and thus these properties are ideally constant with feed pressure, flow rate and other process conditions. However, permeability and selectivity are both temperature-dependent. Accordingly, it is desirable to be able to control the temperature of the hydrocarbons and contaminants before the hydrocarbons and contaminants enter the membrane separator.
It would be desirable to provide an underwater membrane separation system in which the membrane separator is located underwater, such that the temperature of the hydrocarbons and contaminants is controlled to a predetermined temperature by the location of the membrane.
The present invention relates to a system for separating contaminants from hydrocarbons removed from a sub-sea formation. In order to prevent the degradation of the membrane material in the separation system, due to temperature, the present invention provides one or more membrane separators positioned between the production string and the hydrocarbon collection tank in a sub-sea environment wherein the temperature of the hydrocarbons and contaminants is controlled to a predetermined temperature by the location of the membrane.
According to one aspect of the present invention, an underwater membrane separation system with temperature control includes a production string located in a sub-sea wellbore for removing hydrocarbons and contaminants from a sub-sea formation, and at least one membrane separator for separating contaminants from hydrocarbons removed from the sub-sea formation, the membrane separator located underwater between the producing string and a hydrocarbon collection tank, wherein the temperature of the hydrocarbons and contaminants is controlled to a predetermined temperature by the location of the membrane.
According to another aspect of the invention, an underwater membrane separation method with temperature control includes connecting a tube to a sub-sea production string for removing hydrocarbons and contaminants from a sub-sea wellbore, and positioning at least one membrane separator for separating contaminants from hydrocarbons in a tube between the production string and a hydrocarbon collection tank wherein the temperature of the hydrocarbons and contaminants is controlled by the location of the membrane.
According to a further aspect of the invention, a method of controlling a temperature of a production stream of hydrocarbons and contaminants to prevent degradation of a preferentially selective material includes positioning the preferentially selective material underwater at a location selected to achieve a predetermined temperature of the hydrocarbons and contaminants contacting the preferentially selective material.
The present invention provides a system and method for separation of hydrocarbons and contaminants utilizing an underwater membrane separator with temperature control where, by location of the membrane separator, the temperature of the hydrocarbons and contaminants is controlled to a predetermined range optimizing performance of the membrane separator. The system and method also provide reduced downtime and improved efficiency of the membrane separation system.